Cultivation of the brackish-water macroalga Ulva lactuca in wastewater from land-based fish and shrimp aquacultures in Germany

This study aimed to examine the cultivation of the brackish-water macroalga Ulva lactuca L., known as a seaweed with a high growth rate, in a land-based cultivation over 30 days using different aquaculture effluents as medium. The used wastewater was provided by four land-based aquaculture facilities located in Germany, which produced shrimp (Litopenaeus vannamei), catfish (Clarias gariepinus), rainbow trout (Oncorhynchus mykiss) and pikeperch (Sander lucioperca) respectively. Except for an initial solid-liquid separation, the different wastewaters remained untreated and, with the exception of the catfish wastewater, undiluted when used as culture medium. When cultivated in catfish and shrimp wastewater U. lactuca showed maximum growth rates of 4.17% d ⁻¹ (after 10 days) and 3.76% d ⁻¹ (after 20 days) respectively. In comparison, the growth rate of the control group using only Provasoli Enriched seawater medium was approx. 2.65% d ⁻¹. Furthermore, using shrimp wastewater also significantly increased the photosynthetic activity (ETRmax) and the quenching ability (Y(II)) of U. lactuca whereas pikeperch wastewater led to a significant decrease of ETRmax. In contrast, cultivation in catfish and trout wastewater did not affect photosynthetic activity or quenching ability in comparison to the control group.